White clover is a excellent forage for ruminants and is used for grazing, cutting-and-carrying, ensiling and making hay. It is recommended to offer between 20 and 50% white clover in a grass-based diet (cut and carry or grazing), or with a small amount of concentrate in the case of straw-based diet. When pure white clover is to be used (fresh or as silage), a readily fermentable carbohydrate source (for example cereal grain or maize silage) will improve diet utilization.
White clover is highly palatable whether as silage, hay or when grazed at a leafy stage. Physical, chemical and anatomical features contribute to a superior intake of white clover compared with grass (FAO, 2011).
Digestibility and degradability
White clover retains a high digestibility since there is continual generation of new leaves from the stolons, which partially compensates for maturity. In contrast to other forage legumes and grasses, low-digestible stem tissue is not harvested in white clover crops and so digestibility declines less with age than in other species (FAO, 2011). OM and DM digestibility values are generally high, around 80% (Schils et al., 1999; Marshall et al., 2003), but may vary (61 to 82%) according to the stage of phenological maturity (Ayres et al., 1998), or cut number (INRA, 2007). Most of the OM and protein are readily degradable in the rumen (Cohen, 2001). But because of its high protein value, it is recommended to feed white clover forage with a highly digestible OM forage having protein of a lower degradability, such as maize silage.
Pasture or fresh cut-and-carry forage
Many trials have reported the benefits for dairy cows of using white clover in association with grass (mixed pastures or cut-and-carry) or maize silage. It has been suggested that the optimum clover content in pasture may be between 30 and 50% (Caradus et al., 1996; Harris et al., 1997a). Dairy cows grazing pure white clover pasture plus 3 kg DM grass silage had higher milk yield (+ 1.6 to 1.8 L/d/cow) than cows on pure perennial ryegrass without a significant change in milk composition (Caradus et al., 1996). When dairy cows graze a pure tropical pasture or with an increasing proportion of white clover (25 to 75%), milk yields are between 22 and 33% higher with 25% and 50% clover, respectively, than without. Fat content also increases with clover. Including 50% clover in such a pasture is a realistic target to increase milk yield (Harris et al., 1997a; Harris et al., 1997b). Results obtained in Australia show that cows prefer mixed clover/grass pasture than pure clover pasture, allowing them to produce more milk (Rogers et al., 1980 cited by Caradus et al., 1996). When a fresh mixture of perennial ryegrass and white clover (20, 50 or 80%) is fed ad libitum to lactating dairy cows, DM intake and milk yield are significantly higher with 50% clover, but not 80%: 12 kg DM vs. 10.9 kg (DM intake) and 9.8 vs. 8.5 litres (milk yield), respectively. Increasing the clover proportion does not modify milk fat or protein content (Harris et al., 1997a; Harris et al., 1997b). When maize silage partly (50%) replaces fresh white clover, excess N from pure white clover is much better used at the rumen level, reducing ammonia and N urinary excretion without reducing milk yield (Wanjaiya et al., 1993).
When white clover is associated with cocksfoot (Dactylis glomerata) and grazed by growing lambs, it allows a better daily weight gain: 189 vs. 133 g/d measured over 3 years (Papadopoulos et al., 2001). Even a small clover content associated with tall fescue or ryegrass has a large positive effect on live-weight gain of young grazing sheep (Hyslop et al., 2000).
However, meat from animals consuming legume diets has been attributed as having a more intense and less desirable meat flavour than that of animals fed grass diets (Cramer et al., 1967; Shorland et al., 1970 cited by Schreurs et al., 2007). This "pastoral flavour" is due to indole and skatole formed in the rumen from the microbial deamination and decarboxylation of tryptophan (Deslandes et al., 2001).
White clover can partly replace concentrate in a straw-based diet for 20 kg female sheep. When white clover replaced 25 or 50% concentrate, total DMI (expressed as kg W0.75) increased, but not when it replaced 100% concentrate. Dry matter digestibility of the total diet also increased when white clover replaced 25 or 50% of the concentrate and slightly decreased at 100%. Daily weight gain was also higher when the clover replaced 25 or 50% of the concentrate. Consequently white clover beneficially replaced up to 50% of the concentrate in a straw-based diet (Sudesh Radotra et al., 2009).
Pure white clover silage can support 19.6 to 31.5 kg/d of milk without supplementation (Dewhurst et al., 2003; Cohen et al., 2006; Steinshamn et al., 2008). However, when supplemented with a cereal grain (Cohen et al., 2006) or mixed concentrate (Steinshamn et al., 2008), milk yield increased significantly by about 0.6 kg/d of milk per kg concentrate offered. No significant change in fat or protein content was observed (Dewhurst et al., 2003; Cohen et al., 2006) but, when compared to grass silage, white clover (and red clover) silage increased the content of polyunsaturated fatty acids (Dewhurst et al., 2003).
Beef steers (362 kg) fed rye grass silage or white clover silage alone, or mixed with rye grass, showed a higher DM intake (8.4 kg vs. 4.2 kg DM) with clover silage (alone or mixed) compared to pure rye silage. Also, white clover silage increased the flow of linoleic and linolenic acids at the duodenum level, possibly due to reduced biohydrogenation (Lee et al., 2003).